Generally speaking, an engine cooling system comprises a radiator, which is part of a cooling circuit designed to dissipate into the environment the heat which a liquid circulating inside it carries away from the engine, and an axial fan, which generates a forced air flow through the radiator to promote the latter's dissipation of the heat.
The fan may be driven by an electric motor, and comprises an impeller whose rotation is driven by the shaft of the electric motor. A thermostat which detects the temperature of the liquid in the cooling circuit controls activation of the electric motor, which keeps running until the temperature of the cooling liquid detected returns below a predetermined limit value. In other solutions the fan is driven by various types of known actuator devices, for example viscostatic couplings or electromagnetic couplings, whose rotation is in turn driven by the engine.
The impeller comprises a plurality of blades, each with its base secured to a hub which is coaxially fixed to the shaft of the electric motor. The blades extend radially from the hub, may have various profiles and be at various angles to the hub axis of rotation, and in most cases their ends opposite the base are fixed to a stiffening ring, which encloses the blades and is centred on the impeller axis of rotation.
The hub normally has a cylindrical cup shape, so that it at least partly encloses and protects the electric motor.
Axial fans of the type described above have several disadvantages, in particular if used with the cooling circuit of an agricultural vehicle. In the most common working conditions for agricultural vehicles it is quite easy for water, sand and soil to build up in the air space between the electric motor, or the viscostatic coupling, and the impeller hub, creating a sludge that may cause problems with fan operation.